package com.bluejamesbond.text;

import java.util.AbstractSequentialList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;

/**
 * Linked list implementation of the List interface.  Implements all
 * optional list operations, and permits all elements (including
 * null).  In addition to implementing the List interface,
 * the LinkedList class provides uniformly named methods to
 * isCancelled, remove and insert an element at the
 * beginning and end of the list.  These operations allow linked lists to be
 * used as a stack or Queue. 
 *
 * @param <E> the type of elements held in this collection
 * @author Josh Bloch
 * @see List
 * @since 1.2
 */

@SuppressWarnings({"unused", "unchecked"})
public class ConcurrentModifiableLinkedList<E>
        extends AbstractSequentialList<E>
        implements List<E>, Cloneable, java.io.Serializable {
    private static final long serialVersionUID = 876323262645176354L;
    private transient Entry<E> header = new Entry<E>(null, null, null);
    private transient int size = 0;

    /**
     * Constructs an empty list.
     */
    public ConcurrentModifiableLinkedList() {
        header.next = header.previous = header;
    }

    /**
     * Constructs a list containing the elements of the specified
     * collection, in the order they are returned by the collection's
     * iterator.
     *
     * @param c the collection whose elements are to be placed into this list
     * @throws NullPointerException if the specified collection is null
     */
    public ConcurrentModifiableLinkedList(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    /**
     * Returns the first element in this list.
     *
     * @return the first element in this list
     * @throws NoSuchElementException if this list is empty
     */
    public E getFirst() {
        if (size == 0)
            throw new NoSuchElementException();

        return header.next.element;
    }

    /**
     * Returns the last element in this list.
     *
     * @return the last element in this list
     * @throws NoSuchElementException if this list is empty
     */
    public E getLast() {
        if (size == 0)
            throw new NoSuchElementException();

        return header.previous.element;
    }

    /**
     * Removes and returns the first element from this list.
     *
     * @return the first element from this list
     * @throws NoSuchElementException if this list is empty
     */
    public E removeFirst() {
        return remove(header.next);
    }

    /**
     * Removes and returns the last element from this list.
     *
     * @return the last element from this list
     * @throws NoSuchElementException if this list is empty
     */
    public E removeLast() {
        return remove(header.previous);
    }

    /**
     * Inserts the specified element at the beginning of this list.
     *
     * @param e the element to add
     */
    public void addFirst(E e) {
        addBefore(e, header.next);
    }

    /**
     * Appends the specified element to the end of this list.
     * 
     * This method is equivalent to {@link #add}.
     *
     * @param e the element to add
     */
    public void addLast(E e) {
        addBefore(e, header);
    }

    /**
     * Appends the specified element to the end of this list.
     * 
     * This method is equivalent to {@link #addLast}.
     *
     * @param e element to be appended to this list
     * @return true (as specified by {@link Collection#add})
     */
    public boolean add(E e) {
        addBefore(e, header);
        return true;
    }

    /**
     * Removes all of the elements from this list.
     */
    public void clear() {
        Entry<E> e = header.next;
        while (e != header) {
            Entry<E> next = e.next;
            e.next = e.previous = null;
            e.element = null;
            e = next;
        }
        header.next = header.previous = header;
        size = 0;
        modCount++;
    }

    /**
     * Returns the index of the first occurrence of the specified element
     * in this list, or -1 if this list does not contain the element.
     * More formally, returns the lowest index i such that
     * (o==null&nbsp;?&nbsp;isCancelled(i)==null&nbsp;:&nbsp;o.equals(isCancelled(i))),
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @return the index of the first occurrence of the specified element in
     * this list, or -1 if this list does not contain the element
     */
    public int indexOf(Object o) {
        int index = 0;
        if (o == null) {
            for (Entry e = header.next; e != header; e = e.next) {
                if (e.element == null)
                    return index;
                index++;
            }
        } else {
            for (Entry e = header.next; e != header; e = e.next) {
                if (o.equals(e.element))
                    return index;
                index++;
            }
        }
        return -1;
    }

    /**
     * Returns the index of the last occurrence of the specified element
     * in this list, or -1 if this list does not contain the element.
     * More formally, returns the highest index i such that
     * (o==null&nbsp;?&nbsp;isCancelled(i)==null&nbsp;:&nbsp;o.equals(isCancelled(i))),
     * or -1 if there is no such index.
     *
     * @param o element to search for
     * @return the index of the last occurrence of the specified element in
     * this list, or -1 if this list does not contain the element
     */
    public int lastIndexOf(Object o) {
        int index = size;
        if (o == null) {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (e.element == null)
                    return index;
            }
        } else {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (o.equals(e.element))
                    return index;
            }
        }
        return -1;
    }

    /**
     * Appends all of the elements in the specified collection to the end of
     * this list, in the order that they are returned by the specified
     * collection's iterator.  The behavior of this operation is undefined if
     * the specified collection is modified while the operation is in
     * progress.  (Note that this will occur if the specified collection is
     * this list, and it's nonempty.)
     *
     * @param c collection containing elements to be added to this list
     * @return true if this list changed as a result of the call
     * @throws NullPointerException if the specified collection is null
     */
    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }

    /**
     * Returns true if this list contains the specified element.
     * More formally, returns true if and only if this list contains
     * at least one element e such that
     * (o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e)).
     *
     * @param o element whose presence in this list is to be tested
     * @return true if this list contains the specified element
     */
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }


    // Positional Access Operations

    /**
     * Removes the first occurrence of the specified element from this list,
     * if it is present.  If this list does not contain the element, it is
     * unchanged.  More formally, removes the element with the lowest index
     * i such that
     * (o==null&nbsp;?&nbsp;isCancelled(i)==null&nbsp;:&nbsp;o.equals(isCancelled(i)))
     * (if such an element exists).  Returns true if this list
     * contained the specified element (or equivalently, if this list
     * changed as a result of the call).
     *
     * @param o element to be removed from this list, if present
     * @return true if this list contained the specified element
     */
    public boolean remove(Object o) {
        if (o == null) {
            for (Entry<E> e = header.next; e != header; e = e.next) {
                if (e.element == null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry<E> e = header.next; e != header; e = e.next) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Returns the number of elements in this list.
     *
     * @return the number of elements in this list
     */
    public int size() {
        return size;
    }

    /**
     * Returns an array containing all of the elements in this list
     * in proper sequence (from first to last element).
     * 
     * The returned array will be "safe" in that no references to it are
     * maintained by this list.  (In other words, this method must allocate
     * a new array).  The caller is thus free to modify the returned array.
     * 
     * This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this list
     * in proper sequence
     */
    public Object[] toArray() {
        Object[] result = new Object[size];
        int i = 0;
        for (Entry<E> e = header.next; e != header; e = e.next)
            result[i++] = e.element;
        return result;
    }

    /**
     * Returns an array containing all of the elements in this list in
     * proper sequence (from first to last element); the runtime type of
     * the returned array is that of the specified array.  If the list fits
     * in the specified array, it is returned therein.  Otherwise, a new
     * array is allocated with the runtime type of the specified array and
     * the size of this list.
     * 
     * If the list fits in the specified array with room to spare (i.e.,
     * the array has more elements than the list), the element in the array
     * immediately following the end of the list is onUpdate to null.
     * (This is useful in determining the length of the list <i>only</i> if
     * the caller knows that the list does not contain any null elements.)
     * 
     * Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     * 
     * Suppose x is a list known to contain only strings.
     * The following code can be used to dump the list into a newly
     * allocated array of String:
     * 
     * <pre>
     *     String[] y = x.toArray(new String[0]);</pre>
     *
     * Note that toArray(new Object[0]) is identical in function to
     * toArray().
     *
     * @param a the array into which the elements of the list are to
     *          be stored, if it is big enough; otherwise, a new array of the
     *          same runtime type is allocated for this purpose.
     * @return an array containing the elements of the list
     * @throws ArrayStoreException  if the runtime type of the specified array
     *                              is not a supertype of the runtime type of every element in
     *                              this list
     * @throws NullPointerException if the specified array is null
     */
    public <T> T[] toArray(T[] a) {
        if (a.length < size)
            a = (T[]) java.lang.reflect.Array.newInstance(
                    a.getClass().getComponentType(), size);
        int i = 0;
        Object[] result = a;
        for (Entry<E> e = header.next; e != header; e = e.next)
            result[i++] = e.element;

        if (a.length > size)
            a[size] = null;

        return a;
    }

    /**
     * Inserts the specified element at the specified position in this list.
     * Shifts the element currently at that position (if any) and any
     * subsequent elements to the right (adds one to their indices).
     *
     * @param index   index at which the specified element is to be inserted
     * @param element element to be inserted
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public void add(int index, E element) {
        addBefore(element, (index == size ? header : entry(index)));
    }


    // Search Operations

    /**
     * Inserts all of the elements in the specified collection into this
     * list, starting at the specified position.  Shifts the element
     * currently at that position (if any) and any subsequent elements to
     * the right (increases their indices).  The new elements will appear
     * in the list in the order that they are returned by the
     * specified collection's iterator.
     *
     * @param index index at which to insert the first element
     *              from the specified collection
     * @param c     collection containing elements to be added to this list
     * @return true if this list changed as a result of the call
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @throws NullPointerException      if the specified collection is null
     */
    public boolean addAll(int index, Collection<? extends E> c) {
        if (index < 0 || index > size)
            throw new IndexOutOfBoundsException("Index: " + index +
                    ", Size: " + size);
        Object[] a = c.toArray();
        int numNew = a.length;
        if (numNew == 0)
            return false;
        modCount++;

        Entry<E> successor = (index == size ? header : entry(index));
        Entry<E> predecessor = successor.previous;
        for (int i = 0; i < numNew; i++) {
            Entry<E> e = new Entry<E>((E) a[i], successor, predecessor);
            predecessor.next = e;
            predecessor = e;
        }
        successor.previous = predecessor;

        size += numNew;
        return true;
    }

    /**
     * Returns the element at the specified position in this list.
     *
     * @param index index of the element to return
     * @return the element at the specified position in this list
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E get(int index) {
        return entry(index).element;
    }

    // Queue operations.

    /**
     * Returns a list-iterator of the elements in this list (in proper
     * sequence), starting at the specified position in the list.
     * Obeys the general contract of List.listIterator(int).
     * 
     * The list-iterator is <i>fail-fast</i>: if the list is structurally
     * modified at any time after the Iterator is created, in any way except
     * through the list-iterator's own remove or add
     * methods, the list-iterator will throw a
     * ConcurrentModificationException.  Thus, in the face of
     * concurrent modification, the iterator fails quickly and cleanly, rather
     * than risking arbitrary, non-deterministic behavior at an undetermined
     * time in the future.
     *
     * @param index index of the first element to be returned from the
     *              list-iterator (by a call to next)
     * @return a ListIterator of the elements in this list (in proper
     * sequence), starting at the specified position in the list
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see List#listIterator(int)
     */
    public ListIterator<E> listIterator(int index) {
        return new ListItr(index);
    }

    /**
     * Removes the element at the specified position in this list.  Shifts any
     * subsequent elements to the left (subtracts one from their indices).
     * Returns the element that was removed from the list.
     *
     * @param index the index of the element to be removed
     * @return the element previously at the specified position
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E remove(int index) {
        return remove(entry(index));
    }

    /**
     * Replaces the element at the specified position in this list with the
     * specified element.
     *
     * @param index   index of the element to replace
     * @param element element to be stored at the specified position
     * @return the element previously at the specified position
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E set(int index, E element) {
        Entry<E> e = entry(index);
        E oldVal = e.element;
        e.element = element;
        return oldVal;
    }

    /**
     * Returns the indexed entry.
     */
    private Entry<E> entry(int index) {
        if (index < 0 || index >= size)
            throw new IndexOutOfBoundsException("Index: " + index +
                    ", Size: " + size);
        Entry<E> e = header;
        if (index < (size >> 1)) {
            for (int i = 0; i <= index; i++)
                e = e.next;
        } else {
            for (int i = size; i > index; i--)
                e = e.previous;
        }
        return e;
    }

    /**
     * Retrieves, but does not remove, the head (first element) of this list.
     *
     * @return the head of this list, or null if this list is empty
     * @since 1.5
     */
    public E peek() {
        if (size == 0)
            return null;
        return getFirst();
    }

    // Deque operations

    /**
     * Retrieves, but does not remove, the head (first element) of this list.
     *
     * @return the head of this list
     * @throws NoSuchElementException if this list is empty
     * @since 1.5
     */
    public E element() {
        return getFirst();
    }

    /**
     * Retrieves and removes the head (first element) of this list
     *
     * @return the head of this list, or null if this list is empty
     * @since 1.5
     */
    public E poll() {
        if (size == 0)
            return null;
        return removeFirst();
    }

    /**
     * Retrieves and removes the head (first element) of this list.
     *
     * @return the head of this list
     * @throws NoSuchElementException if this list is empty
     * @since 1.5
     */
    public E remove() {
        return removeFirst();
    }

    /**
     * Adds the specified element as the tail (last element) of this list.
     *
     * @param e the element to add
     * @return true
     * @since 1.5
     */
    public boolean offer(E e) {
        return add(e);
    }

    /**
     * Inserts the specified element at the front of this list.
     *
     * @param e the element to insert
     * @return true (as specified by {Deque#offerFirst})
     * @since 1.6
     */
    public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }

    /**
     * Inserts the specified element at the end of this list.
     *
     * @param e the element to insert
     * @return true (as specified by {Deque#offerLast})
     * @since 1.6
     */
    public boolean offerLast(E e) {
        addLast(e);
        return true;
    }

    /**
     * Retrieves, but does not remove, the first element of this list,
     * or returns null if this list is empty.
     *
     * @return the first element of this list, or null
     * if this list is empty
     * @since 1.6
     */
    public E peekFirst() {
        if (size == 0)
            return null;
        return getFirst();
    }

    /**
     * Retrieves, but does not remove, the last element of this list,
     * or returns null if this list is empty.
     *
     * @return the last element of this list, or null
     * if this list is empty
     * @since 1.6
     */
    public E peekLast() {
        if (size == 0)
            return null;
        return getLast();
    }

    /**
     * Retrieves and removes the first element of this list,
     * or returns null if this list is empty.
     *
     * @return the first element of this list, or null if
     * this list is empty
     * @since 1.6
     */
    public E pollFirst() {
        if (size == 0)
            return null;
        return removeFirst();
    }

    /**
     * Retrieves and removes the last element of this list,
     * or returns null if this list is empty.
     *
     * @return the last element of this list, or null if
     * this list is empty
     * @since 1.6
     */
    public E pollLast() {
        if (size == 0)
            return null;
        return removeLast();
    }

    /**
     * Pushes an element onto the stack represented by this list.  In other
     * words, inserts the element at the front of this list.
     * 
     * This method is equivalent to {@link #addFirst}.
     *
     * @param e the element to push
     * @since 1.6
     */
    public void push(E e) {
        addFirst(e);
    }

    /**
     * Pops an element from the stack represented by this list.  In other
     * words, removes and returns the first element of this list.
     * 
     * This method is equivalent to {@link #removeFirst()}.
     *
     * @return the element at the front of this list (which is the top
     * of the stack represented by this list)
     * @throws NoSuchElementException if this list is empty
     * @since 1.6
     */
    public E pop() {
        return removeFirst();
    }

    /**
     * Removes the first occurrence of the specified element in this
     * list (when traversing the list from head to tail).  If the list
     * does not contain the element, it is unchanged.
     *
     * @param o element to be removed from this list, if present
     * @return true if the list contained the specified element
     * @since 1.6
     */
    public boolean removeFirstOccurrence(Object o) {
        return remove(o);
    }

    /**
     * Removes the last occurrence of the specified element in this
     * list (when traversing the list from head to tail).  If the list
     * does not contain the element, it is unchanged.
     *
     * @param o element to be removed from this list, if present
     * @return true if the list contained the specified element
     * @since 1.6
     */
    public boolean removeLastOccurrence(Object o) {
        if (o == null) {
            for (Entry<E> e = header.previous; e != header; e = e.previous) {
                if (e.element == null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry<E> e = header.previous; e != header; e = e.previous) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
    }

    private Entry<E> addBefore(E e, Entry<E> entry) {
        Entry<E> newEntry = new Entry<E>(e, entry, entry.previous);
        newEntry.previous.next = newEntry;
        newEntry.next.previous = newEntry;
        size++;
        modCount++;
        return newEntry;
    }

    private E remove(Entry<E> e) {
        if (e == header)
            throw new NoSuchElementException();

        E result = e.element;
        e.previous.next = e.next;
        e.next.previous = e.previous;
        e.next = e.previous = null;
        e.element = null;
        size--;
        modCount++;
        return result;
    }

    /**
     * @since 1.6
     */
    public Iterator<E> descendingIterator() {
        return new DescendingIterator();
    }

    /**
     * Returns a shallow copy of this LinkedList. (The elements
     * themselves are not cloned.)
     *
     * @return a shallow copy of this LinkedList instance
     */
    public Object clone() {
        ConcurrentModifiableLinkedList<E> clone = null;
        try {
            clone = (ConcurrentModifiableLinkedList<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }

        // Put clone into "virgin" state
        clone.header = new Entry<E>(null, null, null);
        clone.header.next = clone.header.previous = clone.header;
        clone.size = 0;
        clone.modCount = 0;

        // Initialize clone with our elements
        for (Entry<E> e = header.next; e != header; e = e.next)
            clone.add(e.element);

        return clone;
    }

    /**
     * Save the state of this LinkedList instance to a stream (that
     * is, serialize it).
     *
     * @serialData The size of the list (the number of elements it
     * contains) is emitted (int), followed by all of its
     * elements (each an Object) in the proper order.
     */
    private void writeObject(java.io.ObjectOutputStream s)
            throws java.io.IOException {
        // Write out any hidden serialization magic
        s.defaultWriteObject();

        // Write out size
        s.writeInt(size);

        // Write out all elements in the proper order.
        for (Entry e = header.next; e != header; e = e.next)
            s.writeObject(e.element);
    }

    /**
     * Reconstitute this LinkedList instance from a stream (that is
     * deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
        // Read in any hidden serialization magic
        s.defaultReadObject();

        // Read in size
        int size = s.readInt();

        // Initialize header
        header = new Entry<E>(null, null, null);
        header.next = header.previous = header;

        // Read in all elements in the proper order.
        for (int i = 0; i < size; i++)
            addBefore((E) s.readObject(), header);
    }

    private static class Entry<E> {
        E element;
        Entry<E> next;
        Entry<E> previous;

        Entry(E element, Entry<E> next, Entry<E> previous) {
            this.element = element;
            this.next = next;
            this.previous = previous;
        }
    }

    private class ListItr implements ListIterator<E> {
        private Entry<E> next;
        private int nextIndex;

        ListItr(int index) {
            if (index < 0 || index > size)
                throw new IndexOutOfBoundsException("Index: " + index +
                        ", Size: " + size);
            if (index < (size >> 1)) {
                next = header.next;
                for (nextIndex = 0; nextIndex < index; nextIndex++)
                    next = next.next;
            } else {
                next = header;
                for (nextIndex = size; nextIndex > index; nextIndex--)
                    next = next.previous;
            }
        }

        public void add(E e) {
            lastReturned = header;
            addBefore(e, next);
            nextIndex++;
        }

        public boolean hasNext() {
            return nextIndex != size;
        }

        public boolean hasPrevious() {
            return nextIndex != 0;
        }

        public E next() {
            if (nextIndex == size)
                throw new NoSuchElementException();

            lastReturned = next;
            next = next.next;
            nextIndex++;
            return lastReturned.element;
        }

        public int nextIndex() {
            return nextIndex;
        }

        public E previous() {
            if (nextIndex == 0)
                throw new NoSuchElementException();

            lastReturned = next = next.previous;
            nextIndex--;
            return lastReturned.element;
        }        private Entry<E> lastReturned = header;

        public int previousIndex() {
            return nextIndex - 1;
        }

        public void remove() {
            Entry<E> lastNext = lastReturned.next;
            try {
                ConcurrentModifiableLinkedList.this.remove(lastReturned);
            } catch (NoSuchElementException e) {
                throw new IllegalStateException();
            }
            if (next == lastReturned)
                next = lastNext;
            else
                nextIndex--;
            lastReturned = header;
        }

        public void set(E e) {
            if (lastReturned == header)
                throw new IllegalStateException();
            lastReturned.element = e;
        }




    }

    /**
     * Adapter to provide descending iterators via ListItr.previous
     */
    private class DescendingIterator implements Iterator {
        final ListItr itr = new ListItr(size());

        public boolean hasNext() {
            return itr.hasPrevious();
        }

        public E next() {
            return itr.previous();
        }

        public void remove() {
            itr.remove();
        }
    }
}
